1. Field of Invention
The invention relates to the field of visual displays. More particularly, the invention relates to a gyricon or twisting rotatable element visual display having a controlled response to triboelectric charge effects.
2. Description of Related Art
Paper has traditionally been a preferred medium for the presentation and display of text and images. Paper has several characteristics that make it a desirable display medium, including the fact that it is lightweight, thin, portable, flexible, foldable, high-contrast, low-cost, relatively permanent, and readily configured into a myriad of shapes. It can maintain its displayed images without using any electricity. Paper can also be read in ambient light and can be written or marked upon with a pen, pencil paintbrush, or any number of other implements, including a computer printer.
Unfortunately, paper is not well suited for real-time display purposes. Real-time imagery from computer, video, or other sources cannot be displayed directly with paper, but must be displayed by other means, such as by a cathode-ray tube (CRT) display or a liquid-crystal display (LCD). However, real-time display media lack many of the desirable qualities of paper, such as physical flexibility and stable retention of the displayed image in the absence of an electric power source. Electric paper combines the desirable qualities of paper with those of real-time display media. Like ordinary paper, electric paper can be written and erased, can be read in ambient light and can retain imposed information in the absence of an electric field or other external retaining force. Also like ordinary paper, electric paper can be made in the form of a light-weight, flexible, durable sheet that can be folded or rolled into a tubular form about any axis and placed into a shirt or coat pocket, and then later retrieved, re-straightened, and read without loss of information. Yet unlike ordinary paper, electric paper can be used to display full-motion and other real-time imagery as well as still images and text. Thus, electric paper can be used in a computer system display screen or a television.
The gyricon, also called the twisting ball display, rotary ball display, particle display, dipolar particle light valve, rotating element display, etc., provides a technology for making electric paper. A gyricon display is made up of a multiplicity of optically anisotropic rotatable elements, which can be selectively rotated to present a desired surface to an observer. Additionally, a gyricon display can be addressed similarly to other displays to present any desired image or sequence of images.
The optical anisotropy of the gyricon rotatable elements may be provided by dividing each gyricon rotatable element into at least two visible portions. For instance, one portion of the surface of each gyricon rotatable element will have a first light reflectance or color. If only two portions are used then the other portion of the surface of the gyricon rotatable element has a different color or a different light reflectance. One example of this is a gyricon rotatable element which is spherically shaped and has two distinct hemispheres, one black and the other white. Additionally, each light reflectance characteristic or color will have a distinct electrical characteristic, e.g., a zeta potential with respect to a dielectric fluid. Accordingly, the gyricon rotatable elements are electrically as well as optically anisotropic. It is conventionally known that when particles are dispersed in a dielectric liquid, the particles acquire an electric charge related to the zeta potential of their surfaces.
The black-and-white gyricon rotatable elements are embedded in a sheet of optically transparent material, such as an elastomer layer, that contains a multiplicity of cavities. Each of the cavities is permeated by a transparent dielectric fluid, such as a plasticizer. The fluid-filled cavities accommodate the gyricon rotatable elements, one gyricon rotatable element per cavity, to prevent the rotatable elements from migrating within the sheet. Each cavity is slightly larger than the size of the gyricon rotatable element so that each gyricon rotatable element can rotate or move slightly within its cavity.
A gyricon rotatable element can be selectively rotated within its respective fluid-filled cavity by applying an electric field, so that either a specific portion of the gyricon rotatable element is exposed to an observer viewing the surface of the sheet. By applying an electric field in two dimensions, for example, using a matrix addressing scheme, the black and white sides of the rotatable elements for instance can be caused to appear as the image elements, e.g., pixels or subpixels, of a displayed image.
Gyricon displays are described further in U.S. Pat. No. 5,389,945 to Sheridon, incorporated herein by reference in its entirety. The ""945 patent discloses that gyricon displays can be made that have many of the desirable qualities of paper, such as flexibility and stable retention of a displayed image in the absence of power, that are not found in CRTs, LCDs, or other conventional display media. Gyricon displays can also be made that are not paper-like, for example, in the form of rigid display screens for flat-panel displays. Other examples of Gyricon displays are described in U.S. Pat. No. 5,717,514 titled xe2x80x9cPolychromal Segmented Balls For A Twisting Balls Displayxe2x80x9d by Sheridon issued Feb. 10, 1998, U.S. Pat. No. 5,754,332 titled xe2x80x9cMonolayer Gyricon Displayxe2x80x9d by Crowley issued May 19, 1998, U.S. Pat. No. 5,604,027 xe2x80x9cSome Uses Of Microencapsulation For Electric Paperxe2x80x9d by Sheridon issued Feb. 18, 1997, U.S. patent application Ser. No. 08/716,672 titled xe2x80x9cTwisting Cylinder Displayxe2x80x9d by Crowley and Sheridon, filed Sep. 13, 1996, and U.S. Pat. No. 5,894,367 titled xe2x80x9cTwisting Cylinder Display Using Multiple Chromatic Valuesxe2x80x9d by Sheridon, issued Apr. 13, 1999. These describe many variations of gyricon displays including monolayer construction, cylindrical rotating elements, and rotating elements constructed to display more than two colors or constructed as light valves.
Conventional gyricon displays, as described in U.S. Pat. Nos. 4,126,854, 4,143,103, 5,604,027, 5,717,514, 5,894,367, 5,739,801 and 6,055,091, each incorporated herein by reference in its entirety, require a source of electrical power. Gyricon materials respond to the application of high electric fields. However, the electric current requirements can be very low. Basically, the energy required to change the state of the display is the same as that needed to charge the capacitance of the display structure.
As a result, according to this invention, triboelectrically generated charges can be used to write, re-write or erase a gyricon sheet.
This invention provides a gyricon sheet encapsulated between a conducting plate, and a thin, insulating film.
The invention separately provides a gyricon display addressable by a triboelectric charge.
The invention separately provides for erasing an image formed on a gyricon display using a tribo-electric charge.
The invention separately provides a gyricon display that does not require an external electric power source to form or erase an image from the gyricon display.
The invention separately provides a gyricon display having a substrate that is sufficiently conductive to dissipate the small amounts of charge generated by tribo-electric effects.
According to one exemplary embodiment of the electric paper of this invention, a tribo-electric charge induced on the surface of an insulating film generates a sufficient electric field to change the state of one or more gyricon rotatable elements of the electric paper.
According to a second exemplary embodiment of the electric paper of this invention, the tribo-electrically addressable electric paper can be used to form a whiteboard that does not require chalk, solvent based pens or, in fact, any type of pen.
In the exemplary embodiment of the tribo-electrically addressable electric paper of this invention, sufficient electric energy to produce an image is provided by tribo-electric charges stored and dissipated on a surface of the display.
Gyricon displays designed to be addressed by a stylus can sometimes be adversely affected by tribo-electric effects. For example, in the case of gyricon displays typically addressed by an electrically driven stylus, inadvertently contacting the gyricon sheet with the user""s finger rather than with the writing stylus can, under certain conditions, cause rotation of the gyricon rotatable elements due to tribo-electric effects.
In another exemplary embodiment of the electric paper of this invention, the elastomer layer of the electric paper is sufficiently conductive to dissipate small amounts of tribo-electrically generated charge. That is, the elastomer layer effectively discharges the tribo electrically generated charge in a time that is less than that required to cause rotatable element rotation. Intentionally applied voltage, as from a powered voltage source such as a writing stylus, has an effectively infinite supply of charge and will deliver a sustained voltage until the desired writing occurs.
In another embodiment, a gyricon display is provided which can be addressed by depositing an addressing charge on the surface of the display but which dissipates the charge over a small period of time which provides for safe handling of the display after a short period of time without experiencing image destructive tribo-electric effects.